We report on a precise measurement of the electron-antineutrino angular correlation (a coefficient) in free neutron beta-decay from the aSPECT experiment. The a coefficient is inferred from the recoil energy spectrum of the protons which are detected in 4π by the aSPECT spectrometer using magnetic adiabatic collimation with an electrostatic filter. Data are presented from a 100 days run at the Institut Laue Langevin in 2013. The sources of systematic errors are considered and included in the final result. We obtain a=−0.10430(84) which is the most precise measurement of the neutron a coefficient to date. From this, the ratio of axial-vector to vector coupling constants is derived giving ∣λ∣=1.2677(28).
@article{arxiv.1908.04785,
title = {Improved determination of the $\beta$-$\overline{\nu}_e$ angular correlation coefficient $a$ in free neutron decay with the $a$SPECT spectrometer},
author = {M. Beck and F. Ayala Guardia and S. Baeßler and M. Borg and F. Glück and W. Heil and J. Kahlenberg and M. Klopf and G. Konrad and R. Maisonobe and R. Muñoz Horta and C. Schmidt and U. Schmidt and M. Simson and T. Soldner and R. Virot and A. Wunderle and O. Zimmer},
journal= {arXiv preprint arXiv:1908.04785},
year = {2020}
}